The present invention relates to dynamoelectric machines, and more particularly to an improved construction for rotors utilizing squirrel cage windings.
In constructing laminated rotors for induction machines, it is common to interrupt the stack of laminations throughout its length in order to form one or more voids in the rotor. The centrifugal force associated with the spinning rotor gives rise to a radial air flow through these voids, or vents, much in the manner of a centrifugal pump or fan.
In order to form the vents metal spacers are conventionally interposed between laminations. The spacers are usually oriented radially within the rotor stacks so as to impede air flow as little as possible, and defining radial vents. The spacers may take a number of forms; in some motor rotors, they are formed of L-shaped metal strips which are resistance welded to ones of the adjacent laminations. However, a problem arises in the construction of rotors using die-cast squirrel cage windings since the molten metal which forms the rotor bars must be confined within the slots in the stack. Therefore, it has become conventional to provide collar-like spacers formed of strips of steel or the like, which are bent into a closed loop which generally conforms to the cross section of the rotor bar. These collars, or spacers, are then individually attached to laminations to form a gap in the laminations to provide the desired vents, and prevents leakage of molten metal when the rotor bars are formed.
Several deficiencies have been noted in this form of construction. The form and location of the spacers being somewhat imprecise, it has been found necessary to make them somewhat larger than the desired cross section of the actual rotor bars. In this manner any improper forming of the vents or spacers, or inaccurate location upon the laminations, will not diminish the effective cross section of the associated rotor bar. Furthermore, attachment of the spacers is a tedious task, requiring special jigs and fixtures in addition to the equipment normally necessary for the spot welding process.
Another, more basic deficiency in presently-used spacers is their size, i.e. the percentage of the rotor vent periphery which they block. This blockage is caused both by the thickness of the metal used to form the spacers, necessary limitations on the configurations into which they can be formed, and the necessary oversized nature of the spacers as discussed above. Accordingly, it will be understood that it would be highly advantageous to provide an improved spacer design for rotors of electric motors using squirrel cage windings.
It is therefore an object of the present invention to provide an electric motor with a spacer having improved ventilating characteristics.
Another object of the invention is to provide a spacer which can be formed according to desired aerodynamic criteria.
Yet another object is to provide a spacer for a rotor which allows the casting of rotor bars without diminished cross sections, yet itself exhibits minimal width.
Yet another object of the invention is to provide improved spacers which can be fitted to rotor laminations without the need for fusion or adhesive bonding.